Channel Operating Parameters (COP) provide information regarding performance in a communications system. Known methods for operating parameter acquisition are inadequate for modern optical systems due to their expense, high service costs, and inability to provide output in the presence of communication data within acceptable time constraints. In one method applicable to wavelength division multiplexed systems (WDM), a separate monitoring wavelength is provided for the operating parameter data. No other data is transmitted on this wavelength. This method was developed for systems having relatively small bandwidth, for example, systems carrying between 8 and 10 optical channels. As the number of optical channels increases, however, a single wavelength cannot carry sufficient operating parameter information.
In large WDM systems, numerous wavelengths (optical channels) carry data. The wavelengths are typically spread over different frequency bands, and more than one monitoring channel must be provided to monitor each of the frequency bands. The increased number of monitoring channels wastes valuable bandwidth. In addition, introducing multiple monitoring channels upsets signal channel power, and channel spacing becomes critical to minimize four-wave mixing introduced by the monitoring channels.
In another method, operating parameters are acquired and monitored using a carrier frequency modulated by pseudo code. The carrier signal is input to the communications system by multiplying the COP carrier with the data signal, and is recovered at the COP receiver using correlation techniques. The method is typically implemented with loop-back error detection schemes, where the loop-back signals are suppressed (for example, 30 dB) from the data signal. When no data is being transferred on the communication system, this method can deliver error detection measurements in a relatively short time. When data is present, however, the signal to noise ratio is poor and the time for making measurements increases. It is known for measurements to take over eight (8) hours to complete in a single WDM channel. In an N channel system, the loopback steps through each channel sequentially. To test the whole system can require as much as N×8 hours. Such long measurements provide unreliable results.
Furthermore, as the channels in a system increase, the hardware required for the loop-back test also increases. In an N channel optical system, for example, N bays of equipment are required to implement the loop-back according to the method set forth above. The hardware cost in a typical optical system makes this method of measurement undesirable. Also, as the number of channels increases, using the loop-back method increases the likelihood of cross talk, further decreasing the reliability of the test.